The present invention relates to a vehicle powertrain, and more particularly, to a hybrid drive system for motor vehicles.
Automobile manufacturers are actively working to develop alternative powertrain systems in an effort to reduce the level of pollutants exhausted into the air by conventional powertrains equipped with internal combustion engines and to reduce fuel consumption thereof. Significant development has been directed to hybrid electric vehicles. Several different hybrid electric vehicles (HEV) xe2x80x9chave recently been offered for sale. xe2x80x9d These hybrid vehicles are equipped with an internal combustion engine and an electric motor that can be operated independently or in combination to drive the vehicle.
There are two types of hybrid vehicles, namely, series hybrid and parallel hybrid. In a series hybrid vehicle, power is delivered to the wheels by the electric motor which draws electrical energy from the battery. The engine is used in series hybrid vehicles to drive a generator which supplies power directly to the electric motor or charges the battery when the state of charge falls below a predetermined value. In parallel hybrid vehicles, the electric motor and the engine can be operated independently or in combination pursuant to the running conditions of the vehicle. Typically, the control strategy for such parallel hybrid vehicles utilizes a low-load mode where only the electric motor is used to drive the vehicle, an intermediate-load mode where only the engine is used to drive the vehicle, and a high-load mode where the engine and electric motor are both used to drive the vehicle.
Hybrid powertrains have been adapted for use in four-wheel drive vehicles and typically utilize the above-noted parallel hybrid powertrain to drive the primary wheels and a secondary electric motor to drive the secondary wheels. It is desired to provide these four-wheel drive vehicles with an active torque bias front axle for improved vehicle handling and traction control while also providing regeneration during vehicle braking. In addition, improved efficiency and reduction of components is also desirable.
It is an object to the present invention to provide a hybrid powertrain drive system for a four-wheel drive vehicle.
It is another object to the present invention to provide an efficient hybrid drive system which utilizes an increased efficiency automated manual transmission.
It is still another object to, the present invention to provide a four-wheel drive hybrid drive system with an active torque bias front axle for improved vehicle handling and traction control.
These and other objects of the present invention are obtained by providing a hybrid drive system including an engine and an electric motor connected to the engine via a power transfer unit. A first axle assembly is drivingly connected to the electric motor and includes an active clutch system to selectively apply driving torque from the electric motor to a pair of drive axles. A transmission assembly is selectively connected to the engine and is drivingly connected to a second axle assembly. The transmission assembly is engaged with the engine during an engine-driving mode for providing driving torque to the second axle assembly. The transmission assembly is also engaged with the engine for providing driving torque to the second axle assembly and the electric motor is activated to provide driving torque to the first axle assembly while the active clutch system is engaged during a combined engine and electric motor driving mode. The electric motor is activated to provide driving torque to the first axle assembly while the active clutch system is engaged during an electric motor driving mode. In addition, the power transfer unit is engageable during an engine driving mode for driving the electric motor as a generator for generating electricity to charge a battery.
A control unit is provided for controlling the engine, the electric motor, the transmission assembly, the power transfer unit and the active clutch system. The electric motor is operated in a regeneration mode when a braking signal is received by the control unit or at any other time that braking is necessary such as under engine braking conditions in order to give the proper driving feel. The control unit also increases an amount of electric motor torque delivered during a transmission assembly shifting operation in order to reduce shift shock during a shifting operation. The active clutch system includes a pair of active clutches for applying torque to the pair of drive axles as controlled by the control unit. The power transfer unit includes a gear train with a controllable clutch unit.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.